1. Field of the Invention
The present invention relates to a heat-sensitive recording material using a diazo compound and a coupler in combination as color-developing compounds, and particularly to a diazo heat-sensitive recording material which, after recording, exhibits excellent light-fastness with image and non-image areas.
2. Description of the Related Art
A diazo compound (diazonium salt compound) reacts with a compound called a coupler, such as phenol derivatives or compounds having an active methylene group, to form an azo dye. When irradiated with light, diazo compounds decompose and lose activity. Because of this property, diazo compounds have long been used as photosensitive recording materials; especially diazo copy (The Society of Photographic Science and Technology of Japan, "Basics of Photographic Engineering--Non-silver Salt Photography-" Corona Publishing Co., Ltd. (1982), pp. 89-117, 182-201).
Recently, diazo compounds have also been applied to recording materials which require fixation of an image. As a typical example of such application, there can be mentioned a light-fixation type heat-sensitive recording material in which a diazo compound and a coupler are heated and reacted in accordance with an image signal so as to form an image. Subsequently the thus-formed image is irradiated with light in order to be fixed (Koji SATO, et al. "The Journal of the Institute of Image Electronics Engineering of Japan" Vol. 11, No. 4 (1982), pp. 290-296).
However, these recording materials have the drawback of a relatively short shelf life since even when stored in a dark place, active diazo compounds gradually decompose thermally and thus lose reactivity. In order to solve this problem, there is proposed a method in which a diazo compound is contained in a microcapsule so as to isolate the diazo compound from water, bases, and similar compounds which would otherwise decompose the diazo compound. This method enables a recording material to dramatically increase its shelf life (Tomomasa USAML et al. "Journal of The Electrophotography Society" Vol. 26, No. 2 (1987), pp. 115-125).
A microcapsule having a glass-transition temperature higher than room temperature does not allow substances to enter through the wall at room temperature. It only allows substances to enter the wall at the glass-transition temperature or above, and thus can be applied as a heat-responsive microcapsule to a heat-sensitive recording material. Accordingly, a recording material comprising a support having a heat-sensitive recording layer coated thereon in which the heat-sensitive recording layer contains a diazo compound encapsulated in a heat-responsive microcapsule, a coupler, and a base enables: (1) the diazo compound to be stably stored over a long period of time; (2) an image to be color-developed through application of heat; and (3) an image to be fixed through irradiation with light.
Recently, there have been developed heat-sensitive recording materials of this kind having advanced functions for forming multicolor images (Japanese Patent Application Laid-Open (JP-A) Nos. 4-135787 and 4-144784). Improved performance is desired in such heat-sensitive recording materials having advanced functions. As is fundamentally improved raw stock storability before use for recording, and improved light-fastness with image and non-image areas after use for recording.
For example, there are proposed methods of using a cyclic 1,3-diketone compound as a coupler in order to obtain a red image (Japanese Patent Application Laid-Open (JP-A) Nos. 2-54250 and 2-54251).
However, these methods fail to sufficiently provide the above-described performance or improvements.